Apparatus for and method for bending glass sheets

ABSTRACT

An apparatus for press bending glass sheets, the apparatus comprising an upper die, a suspension system for the upper die for suspending and vertically moving the upper die, a lower gravity bending mould and a plurality of spacer devices for spacing the upper die and the lower mould a selected distance from each other when the upper die presses a glass sheet on the lower mould, the suspension system being adapted and the spacer devices being configured to permit lateral movement of the die relative to the mould. There is also provided a method of press bending glass sheets.

BACKGROUND TO THE INVENTION

The present invention relates to an apparatus for and a method ofbending glass sheets and more particularly to the bending of glasssheets in which there is an initial gravity bending step and asubsequent press bending step. The apparatus and method are particularlyuseful for bending automotive glass for subsequent laminating, forexample to manufacture vehicle windshields.

DESCRIPTION OF THE PRIOR ART

Glass for the windows of vehicles is normally curved, the curvaturebeing imparted to planar glass by a bending process. In one such bendingprocess planar glass sheets are placed upon female ring moulds andheated to the glass softening point. Each sheet bends ("sags") under itsown weight until the periphery of the glass sheet is in contact with thering mould. Such a bending technique is known as "sag" or gravitybending, and it has been developed over the years so as to bend glasssheets which meet the demands of vehicle manufacturers.

For example, as more deeply bent glass was required, the ring mould wasmodified by attaching the ends of the mould to the central portion byhinges, the hinged mould ends or wing portions progressively closing asthe glass softened and the bend proceeded. This avoided the tendency forthe glass sheet to slide relative to the mould during the bend, therebypreventing scratching. Such a mould is commonly termed an articulatedmould.

The gravity bending process has been found particularly suitable for theproduction of glass that is to be subsequently laminated by combiningtwo sheets of glass with a sheet of interlayer material. The gravitybending process is capable of producing glass to a high optical quality,and it is also possible to bend two sheets of glass simultaneouslythereby producing a matched pair of glasses which give an excellent fiton laminating.

In recent years, developments in vehicle design have required glass ofcomplex curvature, i.e. glass that is bent in two directions generallyat right angles to each other. It is not possible to impart more than avery limited degree of complex curvature to a sheet of glass by gravitybending alone.

Furthermore, increased use of automated assembly by vehiclemanufacturers demands that tighter dimensional tolerances be met by theglass. The shape of the periphery of the bent pane must be accurate, notonly in terms of its two dimensional projection, but also in threedimensions, i.e. the angle of the glass adjacent the periphery must becorrect. If this "angle of entry", as it is known to those skilled inthe art, is not correct, the bent pane will not fit and sealsatisfactorily in the receiving flange of the vehicle bodywork.

Moreover, the optical properties of the window depend on the shape ofthe central region of the glass which must therefore by accuratelycontrolled in order that the required optical standards may be met.

These requirements, in conjunction with the trend towards deeper, andmore complex bends, can no longer be met by glass bent by the gravitybending technique alone. It is now regarded as necessary to complete thebending of such shapes by a subsequent press bending step. This step mayonly involve a limited part of the area of the bent pane, for instancethe areas that, after installation in a vehicle body, will be adjacentthe windscreen pillars of said body. In many current vehicle designs,such areas of the pane are required to be more deeply bent, and in thisspecification, any area of a pane which is required to be more deeplybent by means of a subsequent press bending step will be referred to asa deep bend portion.

In the press bending step, an upper mould or die is lowered onto theupper surface of the glass sheets to that the glass sheets are furtherbent by the action of the upper mould pressing the sheets against alower mould. When the press bending step is carried out after initialgravity bending, the lower mould may comprise the gravity bending mould.

Press bending is also employed in the art to bend planar glass sheetswithout initial gravity bending. However, this can lead to disadvantagesin that because the bent profile is achieved by an applied pressingforce by squeezing individual sheets between two moulds, the optical andphysical properties of the glass sheets can be reduced as compared togravity bending. Also, stresses may be induced in the glass sheets whichcan cause breakage or require an additional annealing step to removethem. Accordingly, the apparatus and methods employed in press bendingalone i.e. not following a gravity bending step, can be different fromthose employed in subsequent press bending following initial gravitybending.

U.S. Pat. No. 5,059,235 discloses an apparatus for bending glass sheetsin which an upper mould or die is mounted for vertical movement above alower mould. The upper die is supported by three vertical rods mounted,via universal joints, in a triangular configuration to a plate providedon the upper surface of the die. The three rods are supported by cableswhich in turn are fed over pullies lies and connected to respectivepiston rods of respective hydraulic or pneumatic cylinders. Centeringpins provided in conjunction with the upper die which cooperate withcorresponding centering openings which are provided in conjunction withthe lower mould. The centering devices act to fix the position of theupper die relative to that of the lower die during the press bendingoperation. This specification does not disclose a bending apparatusconfigured to be used in a press bending step subsequent to an initialgravity bending step. There is no disclosure of a press bendingapparatus for use in a loop in which a plurality of gravity bendingmoulds are cycled in succession around the loop. The apparatus disclosedin the specification would suffer from the technical problem that theprovision of centering devices which fix the position of the upper mouldrelative to the lower mould, both translationally and rotationally,could result in problems in correctly performing the press bendingoperation because the positions of the gravity bending moulds can varysignificantly in a horizontal plane from one mould to another. Althoughthe mounting of the rods through the furnace roof does permit verylimited lateral movement of the rods, the centering devices limit thelateral freedom of the two moulds relative to each other. Furthermore,the specific configuration of the centering devices, comprising pinswhich are required to descend into openings, require the two moulds tobe substantially parallel when the two moulds come into contact. Thismay be difficult to achieve in a loop incorporating a plurality ofgravity bending moulds wherein the height and tilt of the gravitybending moulds can vary from one mould to another.

U.S. Pat. No. 4,661,141 discloses an apparatus for press bending flatglass sheets in which an upper mould is lowered onto a lower articulatedmould. The lower mould is provided with adjustable stops that limit themovement of the upper and lower moulds toward each other. The stopsinclude a stop member having a threaded shank threaded into a hole inthe associated lower mould. The stop member has a flat upper surfacewhich bears against the lower curved surface of the upper mould and theaxis of the threaded shank is inclined to the vertical. The apparatusdisclosed in the specification does not relate to a bending loop inwhich a plurality of gravity bending moulds are successfully cycledaround the loop with a subsequent press bending step being carried outafter the initial gravity bending step. The stop member configurationdisclosed in the specification is not configured so as to accommodatelateral or tilting movement of the die relative to the lower mould,which tends to occur when a plurality of gravity bending moulds areprovided with can vary in position from one to another,

U.S. Pat. No. 5,045,101 discloses an apparatus for bending glass sheetsin which stopper pieces are arranged to set a gap between an upperpressing die and a lower mould. A stopper rod is provided to adjust thevertical position of an arm carrying a pressing die and a lengthadjustable rod is employed to set a predetermined distance between thepressing die and the underlying lower mould. This is a relativelycomplicated arrangement which is relatively cumbersome to employ in abending loop in which a plurality of gravity bending moulds areemployed,

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simple yet effectivemeans for spacing an upper die relative to a lower mould during a pressbending operation which can accommodate any lateral displacement of theupper mould die relative to the lower mould which is required when aplurality of gravity bending moulds are cycled successively around abending loop. Another object of the present invention is to provide ameans for spacing the upper die relative to the lower mould whichpermits freedom of movement both translationally and rotationally of theupper die relative to the lower mould if the upper die is lowered ontothe lower die at an angle to the horizontal, which can occur as a resultof different positions and heights of the lower gravity bending mouldsfrom one to another around the bending loop.

The present invention provides an apparatus for press bending glasssheets, the apparatus comprising an upper die, a suspension system forthe upper die for suspending and vertically moving the upper die, alower gravity bending mould and a plurality of spacer devices forspacing the upper die and the lower mould a selected distance from eachother when the upper die presses a glass sheet on the lower mould, thesuspension system being adapted and the spacer devices being configuredto permit lateral movement of the die relative to the mould.

The present invention further provides a method of press bending glasssheets, the method comprising the steps of providing a gravity bentglass sheet carried on a gravity bending mould; lowering an upper die bya suspension system onto the glass sheet, the upper die having a lowersurface to mould the glass sheet to a desired curved shape, andreleasing the upper die from being supported by the suspension system sothat the upper die rests on the glass sheet at a selected net weightduring a press bending operation, the upper die being spaced above thelower die by a predetermined distance defined by a plurality of spacerdevices; and wherein during the lowering step the upper die isunconstrained against lateral and tilting movement so that the upper dieis permitted progressively to be aligned with the bent glass sheet asthe upper die comes into contact with the bent glass sheet, the spacerdevices being adapted to permit said lateral and tilting movement of theupper die.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic part-sectional side view through a furnace forheating glass sheets showing a gravity bending mould carrying a pair offlat glass sheets prior to a gravity bending operation;

FIG. 2 is an enlarged schematic part-sectional side view of one of thewing locking devices shown in FIG. 1;

FIG. 3 is a schematic part-sectional side view on line A--A of FIG. 2;

FIG. 4 is a plan view of the gravity bending mould mounted on a base ina carriage as illustrated in FIG. 1;

FIG. 5 is a schematic part-sectional side view, similar to that of FIG.1, showing an apparatus for press bending glass sheets in the furnace,the apparatus being illustrated prior to a press bending operation;

FIG. 6 shows the apparatus of FIG. 5 during a press bending operation;and

FIG. 7 is an enlarged side view of one of the spacer devices illustratedin FIG. 6.

DETAILED DESCRIPTION 0F THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a section through a tunnel furnace 2for bending glass sheets, typically a pair of glass sheets 4 which,after the bending operation, are intended to be laminated together inorder to manufacture, for example, an automobile windshield. Such atunnel furnace 2 is well known in the art and consists of an elongatetrack 6 carrying a succession of wheeled open-topped carriages 8thereon. Each carriage 8 has a gravity bending ring mould 10 therein,the mould 10 being mounted on a base 12 which is fixed to a solid bottomwall 14 of the carriage 8. The carriage 8 also has an annular,preferably rectangular, side wall 9. The carriages 8 are mounted insuccession for cyclical movement around a loop including the furnace 2.The loop includes a glass loading zone, a heating zone in which theheated glass sheets are gravity bent on the gravity bending mould 10, acooling zone, and a glass unloading zone. The furnace 2 may be providedwith other zones, for example an annealing zone, for annealing the glassso as to reduce stresses generated during the bending step, between theheating zone and the cooling zone. It will be understood by the skilledperson that although the present invention is exemplified by a boxfurnace, the present invention can alternatively be employed in anyother type of lehr.

The present invention is particularly concerned with the manufacture ofglass sheets having deep bend portions which cannot readily be achievedby the use of gravity bending alone. In accordance with the invention, apress bending zone is additionally provided in the loop immediatelydownstream of the gravity bending zone. In the press bending zone, thegravity bent glass sheets are further press bent to a final desiredshape by an upper reciprocable mould while the glass sheets aresupported on the gravity bending mould.

FIG. 1 illustrates glass sheets 4 on the mould 10 in a carriage 8 priorto the gravity bending operation. The carriage 8 is arranged to movealong the furnace 2 in a direction at a right angle to the plane of thedrawing. The mould 10 comprises a central fixed mould portion 16 whichis mounted to the mould base 12 by a plurality of supports 18. Onopposed sides of the central portion 10 of the mould 8 are hingedlymounted respective articulated wing portions 20. Although the inventionis described with reference to a gravity bending mould having twoopposed wing portions, it will be apparent to those skilled in the artthat the invention could also utilise a gravity bending mould havingonly one articulated wing portion. The wing portions 20 are arranged tomove by rotation between a lower position, as shown in FIG. 1, whereinthe mould 10 is configured support one or more flat glass sheets 4 onthe mould 10, and a higher position at which the wing portions 20define, together with the central portion 16, a continuous curvedannular rim defining a surface to by attained by the glass sheet orsheets 4 when finally bent. The glass sheets 4 are heated as they passthrough the heating zone of the furnace 2 so that the glass sheets 4 areprogressively softened and sag under the effect of gravity so as toconform to the desired shape as defined by the mould 10. Above thecentral portion 16 of the mould, the glass sheets 4 sag until they restagainst the upper mould surface thereby conforming to the desired shape.Above the wing portions 20, the effect of the softening of the glasspermits the wing portions 20 to be articulated upwardly under the actionof an applied force provided by a pair of counterweights so that eachwing portion 20 rotates about a respective pivot axis 22 at the juncturebetween the central portion 16 and the respective wing portion 20 sothat the glass sheets 4 are pushed upwardly and are progressively bentuntil the bottom surface of the glass sheets 4 rests against the uppersurface of the wing portions 20. As will be described hereinafter, whendeep bend portions are present in the glass sheets, those portions tendto require to be mechanically pressed against the lower mould by anupper die or mould so that the desired shape defined by the lower mouldis reliably and repeatably achieved. It will be apparent that thepresent invention may employ so-called "weightless" moulds which do nothave counterweights but rather are specially configured so that themould articulates under the action of the weight of the glass as itsoftens.

A typical mould 10 is illustrated in greater detail in FIG. 4. The mould10 is mounted above the base 12 by the supports 18 which are fixed tothe underside of the central portion 16 of the mould 10. The base issufficiently rigid so as to minimise deflection during the subsequentpress bending step. The wing portions 20 are connected to the centralportion 16 on opposed sides thereof by respective pivot axes 22. Eachwing portion 20 has mounted thereto on opposed sides thereof a pair ofcounterweights 24, each counterweight 24 being mounted on a respectivearm 26 which is fixed to a respective end 28 of a respective pivot axes22. The upper surface of the rim 30 of the mould 10 formed by thecentral portion 16 and the wing portions 20 contacts the underside ofthe glass sheets 4 and defines a final desired shape for the glasssheets 4. The surface area of the mould 10 contacting the glass sheets 4is preferably minimized so as to reduce the area available for heattransfer between the glass sheets 4 and the metal mould 10 which canlead to undesirable stresses being present in the finally bent glasssheets 4 and/or visible defects being present in the edges of the glasssheets 4. Such stresses can cause breakage of the glass sheets 4.Typically, it is desired to keep tensile area stresses in the glasssheets to less than 7 MPa. Typically, the annular rim 30 of the mould 10defined by the upper surfaces of the central portion 10 and the wingportions 20 has a thickness of from about 3 to 4 mm so as to minimisethe area of contact between the glass and the mould 10. However, when,in accordance with the present invention, the gravity bending mould 10is intended to be employed as the lower mould in a subsequent pressbending operation, it is required for the lower mould to be sufficientlyrigid and strong so that it does not uncontrollably deflect or distortunder the action of the applied pressure from the upper press bendingmould. It is also required that the thin rim does not mark the undersideof the glass during the press bending operation.

In accordance with the present invention, the glass sheet bendingapparatus is especially adapted so as to permit a conventional sagbending mould having a relatively thin annular rim to be employed in asubsequent press bending operation whilst ensuring high quality controlof the finally bent glass sheet products. The use of such a thin annularrim provides low stresses in the glass as described hereinabove.Modifications have been made to the mould and to remaining parts of theapparatus so as to ensure that the mould reliably ensures that therequired final shape is achieved, the mould can withstand the pressbending operation and the glass sheets are not inadvertently marked orotherwise deteriorated in quality as a result of the additional pressbending operation.

Referring back to FIG. 1, the wing portions 20 are each provided with atleast one locking device for vertically locking the position of the wingportion during the press handing operation. Optionally, each wingportion has two locking devices although the illustrated embodiment isonly provided with one locking device for each wing portion. The lockingdevice comprises a hinged locking arm 32 which is hingedly mounted tothe respective wing portion 20 and depends downwardly therefrom so as tobe able to slide over the top surface of a plate 34, mounted on the base12, which provides an upper cam surface.

The locking arm 32/plate 34 assembly is shown in greater detail in FIGS.2 and 3. The locking arm 32 comprises a pair of elongate spaced plates36 which are hingedly mounted at their upper ends to an extension member38 fixed to the respective wing portion 20, the extension member 38passing between the plates 36 and the pivotal mounting therebetweencomprising a bolt assembly 40. The locking arm 32 depends downwardlyfrom the wing portion 20 and the free bottom end 42 thereof is providedwith a cylindrical spacer 44 which is fixed between the plates 36 by afurther bolt assembly 46. The cylindrical spacer 44 is clamped betweenthe elongate plates 36 so as to be prevented from rotational movementrelative thereto. A further spacer 48 and bolt assembly 50 are providedsubstantially at the centre of the locking arm 32.

The locking arm 32 is free to pivot relative to the wing portion 20about the extension member 38 and the lower surface 52 thereof rests onthe upper surface of the plate 34 which comprises an elongate camsurface 54 over which the free bottom end 42 of the locking arm 32 canslide. The cam surface 54 comprises a substantially horizontal portion56 and an adjacent inclined ramp portion 58. The ramp portion 58 ispreferably inclined at an angle of around 20° to the horizontal and ifdesired the substantially horizontal portion 56 can be slightly inclinedto the horizontal by a few degrees in the same sense as the ramp portion58. The plate 34 is adjustably mounted in an upright configuration tothe base 12 via a mounting plate 60 to which the plate 34 is removablysecured by bolt assemblies 62. The plate 34 can readily be adjusted inheight and tilt.

In FIG. 1, the wing portion 20 is shown in its lowered configuration andin this configuration the locking arm 32 is inclined to the horizontalin an unlocked position and the free end 42 thereof rests on the rampportion 58 of the cam surface 54 of the plate 34. Such a configurationis illustrated in phantom in FIG. 2. During the gravity bending step,the wing portion 20 rotates upwardly under the action of thecounterweights 24 which progressively causes the glass sheet to beincreasingly bent as it softens on heating. The wing portion 20 movesfrom the phantom position illustrated in FIG. 2 to the position shown bythe solid lines in FIG. 2. It will be seen that as the wing portion 20rises during the gravity bending step, the free end 42 of the lockingarm 32 slides upwardly along the ramp portion 58 Until it reaches thesubstantially horizontal portion 56 which defines a locking zone 64 forthe locking arm 32. The locking arm 32 moves in a plane perpendicular tothe pivot axis 22. As is shown in FIG. 4, the plate 34 defining the camsurface 54 is at right angles to the respective pivot axis 22 so that asthe wing portion 20 is rotated upwardly about the respective pivot axis22, the free end 42 of the locking arm 32, and in particular the lowersurface 52 of the spacer 44, slides steadily up the ramp portion 58until the locking arm 32 is substantially vertical, with the free end 42thereof being positioned in contact with the locking zone 64. As shownin FIG. 2, in order to ensure that the locking arm 32 does notinadvertently move laterally off the cam surface 54, a wire 66 connectedat opposed ends 68 thereof to respective opposed ends 70 of the plate 34and which passes between the spaced plates member 36 of the locking arm32 may be provided.

As shown in FIG. 2, the locking arm 32 in its locking position issubstantially vertical. Preferably, the height and inclination of theplate 34 is adjusted so that in the locking position the locking arm 32is not quite vertical but is a few degrees slightly inclined to thevertical, the inclination being in the same sense as that for theunlocked position. In the locking position the lower surface 52 of thenon-rotatable spacer 44 frictionally engages the cam surface 54 in thelocking zone 64. Since the locking zone 64 is substantially horizontaland the locking arm 32 is substantially vertical, during the subsequentpress bending operation, which is described in detail hereinafter, inwhich a downward pressing force is applied to the wing portion 20 in itsupwardly rotated position, a corresponding force is transmitted downthrough the locking arm 32 and thence to the base 12 through the plate34 and the mounting plate 60 to which the plate 34 is mounted. Such adownward pressing force on the wing portion 20 is transmitted withminimal downward deflection or distortion of the wing portion 20. Thelocking arm 32 acts as a rigid and locked support strut for the wingportion 20 as a result of the frictional engagement between the lockingarm 32 and the locking zone 64 of the cam surface 54. This enables anarticulated mould 10 having a relatively thin annular rim 30 to beemployed in a subsequent press bending operation.

It will be appreciated that an operator is required to set up thelocking arm 32/plate 34 assembly when the apparatus is cold. However,the apparatus is required to operate satisfactorily and reliably atelevated temperatures in the furnace, for example at around 600° to 650°C. The initial setting up must take account of expansion of the variousparts of the apparatus on heating as well as slight distortion of themechanical parts as a result of thermal cycling and also mechanical wearover time. It is obviously preferred that the apparatus be easy to beset up by an operator. Accordingly, the locking arm 32/plate 34 assemblyis preferably configured so that the locking arm 32 is not quitevertical in the press bending step. This ensures that even if distortionand wear were to occur, the locking arm 32 could not rotate past thevertical position and slide off the end 70 of the plate 34. Thisadditionally permits over a large number of heating cycles, a range ofpotential locking positions to be defined along the locking zone 64corresponding to a range of slightly varying heights (relative to thebase 12) of the the wing portion 20 to which the locking arm 32 isattached. This can readily compensate for any distortion and wear whichmay occur as a result of successive thermal cycles. The final angularposition and thus the height of the wing portion 20 is defined by stopmembers on the arms 26 carrying the counterweights 24 which define afinal position for the mould corresponding to the final desired shape ofthe glass sheets. However, it is possible for the height of the wingportion 20 slightly to vary with respect to the base 12 as a result ofthermal cycling and the provision of a locking range ensures that thelocking arm operates to act as a support strut for the wing portion 20of the mould 10 during the press bending operation despite such thermalcycling having caused a slight change in the final angular position ofthe locking arm 32. This obviates the need for regular checking andadjustments to the locking devices. Preferably, the locking zone 64 isinclined slightly upwardly so as to permit smooth sliding movement by acamming action of the free end 42 of the locking arm 32 along the camsurface 54. The locking arm 32/plate 34 assembly is easy to set upmanually merely by adjusting the height and orientation of the plate 34relative to the base 12, and thus relative to the locking arm 32 on therespective wing portion 20.

The final configuration of the mould 10 after the gravity bendingoperation and prior to the press bending operation is illustrated inFIG. 5.

Although the embodiment illustrated in FIGS. 1 to 4 shows only onelocking arm mounted on each wing portion 20, if desired two or morelocking arms may be provided on each wing. After the press bendingoperation which is described hereinafter, and after the press bent glasssheets have been removed from the mould at the unloading zone, the wingportion 20 can be reset to its initial lower configuration by anoperator manually pushing the locking arm 32 inwardly so as to disposedin the configuration illustrated in phantom in FIG. 2. If desired, thisoperation could be performed automatically, for example by a robot.

Referring to FIG. 5, there is shown the press bending apparatus,designated generally as 72, at the press bending zone in the tunnelfurnace 2, the press bending apparatus 72 being illustrated prior to thepress bending operation. At the press bending zone, the carriage 8containing the mould 10 carrying the gravity bent glass sheets 4, withthe wing portions 20 being disposed in their upwardly rotatedorientation and with the locking arms 32 being in a substantiallyvertical orientation and bearing downwardly against the upper surface ofthe respective plates 34 as described hereinabove, is conveyed to apre-set position at which the glass sheets 4 are positioned so as to bedisposed beneath the press bending apparatus 72. The press bendingoperation is employed when it is desired to complete the bending of theglass sheets 4 to the required shape so that the resultant finally bentglass sheets 4 have a shape defined by the gravity bending mould 10.

The press bending apparatus 72 comprises an upper mould or die 74 havinga lower mould surface 76 which constitutes a male mould surfacesubstantially corresponding to the female mould surface defined by thegravity bending mould 10. The glass sheets 4 are intended to be pressbent between the upper mould 74 and the gravity bending mould 10 so asto attain the required shape. The upper mould 74 preferably comprises aceramic body. As shown in FIG. 5, the upper mould 74 may comprise aunitary mould. However, in alternative configurations the upper mould 74may comprise a pair of spaced mould parts which are arranged to bepressed against only those portions of the glass sheets 4 which arerequired to be deeply bent i.e. in the vicinity of the wing portions 20.

The upper mould 74 is supported by a sub-frame 78. The sub-frame 78depends downwardly from a support frame 80 by a plurality of chains 82.Preferably, there are four chains 82, each located at a respectivecorner of the upper mould 74. Metal cables may be employed instead ofchains. The support frame 80 has connected to the upper surface 84thereof a cable (or chain) 86 which extends upwardly from the centre ofthe support frame 80 through the roof 87 of the tunnel furnace 2, over afirst pulley 88 so as to be substantially horizontal, over a secondpulley 90 so as to depend vertically downwardly with the end of thecable 86 being connected to a first counterbalance 92 which is in turnconnected to a die moving mechanism 94. The counterbalance 92 and thedie moving mechanism 94 are located laterally adjacent the tunnelfurnace 2 on one common longitudinal side thereof. The die movingmechanism 94 preferably comprises a hydraulic or pneumaticpiston/cylinder assembly which is connected at the bottom end thereof tothe floor 96. In FIG. 5, the upper mould 74 is illustrated in its raisedconfiguration with the piston/cylinder assembly 94 being in a retractedconfiguration. In the raised configuration of the upper mould 74, thecarriage 8 can be moved from an upstream part of the tunnel furnace 2into position beneath the upper mould 74 prior to the subsequent pressbending operation. The counterbalance 92 is provided with a desiredweight so as to minimize the work required to be expended by thepiston/cylinder assembly 94 in raising and lowering the upper mould 74but with the proviso that in the event of failure of the piston/cylinderassembly 94, th weight of the first counterbalance 92 is sufficientlyhigh so that the entire apparatus fails safely so as to pull the uppermould assembly 74 upwardly away from the carriages 8 passing thereunder.

A second counterbalance assembly is also provided for permitting theupper mould 74 to rest on the glass sheets 4 during the press bendingstep with a predetermined net weight. A rigid metal rod 98 extendsupwardly away from the centre of the upper surface 100 of the sub-frame78 for the upper mould 74. A second cable 102 is connected to the upperpart of the rod 98 and extends successively through holes (not shown) inthe support frame 80 and the furnace roof 87, and thence over a pair ofpulleys 104,106 so as to be connected to at the other end thereof to asecond counterbalance 108 which is free to move vertically. If desired,for both the first and second counterbalances 92,108 vertical rails orsupports (not shown) may be provided so as to prevent inadvertentlateral movement of the counterbalances 92,108. The secondcounterbalance 108 has a specific weight which is selected so as toprovide a specific predetermined net weight to the combined assembly ofthe upper mould 74 and the sub-frame 78 to which the mould 74 ismounted. The net weight of the upper die assembly is typically from 50to 100 kg depending on the particular mould configuration and the sizeand desired shape of the bent glass sheets. The cable 102 between thesecond counterbalance 108 and the upper mould 74 is always in tension.The metal rod 98 is provided between the cable 102 and the sub-frame 78so as to reduce inadvertent stretching or deformation of the cable 102in the vicinity of the upper mould 74 where the ambient temperature inthe pressing zone is high. The cable 86 between the mounting frame 80and the first counterbalance 92 is also always in tension. As describedhereinbelow, during the press bending step the chains 82 are permittedto go slack so that during the press bending operation it is only theselected net weight of the upper mould 74 and its associated sub-frame78 which is applied to the upper surface of the glass sheets 4.

On opposed sides of the upper mould 74 and adjacent thereto are provideda plurality of spacer devices 109. The spacer devices 109 each includean upper stop member 110, comprising a vertical body 112 having fixedthereto at the bottom end thereof a substantially horizontal plate 114.The upper stop members 110 are firmly mounted on the sub-frame 78. Acorresponding plurality of lower stop members 116 of the spacer devicesare mounted on the base 12. Each lower stop member 116 comprises anupwardly extending body 118 having mounted at its upper end a verticallyadjustable spacer member 120. As is shown in greater detail withreference to FIG. 7, each spacer member 120 comprises a bolt portion 122having a domed head portion 124 which is substantially hemispherical andthe upper surface of which is arranged, during the press bendingoperation, to bear against the lower surface 126 of the plate portion114 of the respective upper stop member 110. The bolt portion 122 isthreaded into the upwardly extending body 118 so as to be readilyadjustable in height and a threaded nut 128 is provided so as to permitfixing of the domed head portion 124 at the required height. Preferably,the plate portion 114 and the domed head portion 124 are composed ofsteel. The upper and lower stop members 110,116 are provided in registryin pairs. Preferably, three pairs of stop members 110,116 are provided.With such a configuration, as is shown in FIG. 4, two pairs of stopmembers are provided on one long edge 117 of the mould 10 in spacedrelation and a third pair of stop members 110,116 is provided centrallyalong the opposite long edge 119 of the mould 10.

The spacer devices 109 are provided so as to ensure that the upper andlower moulds 74,10 are separated over substantially their entire area bya gap corresponding to the thickness of the glass sheets 4 in theirfinal shaped form. This ensures that any over-pressing of the glasssheets 4, which can result in marking of the glass sheets 4 by theannular rim 30, is substantially avoided. As is described in detailhereinafter, three spacer devices 109 are preferably provided so that itis ensured that the vertical position of the upper mould 74 relative tothe lower gravity bending mould 10 is determined without inadvertentrelative rocking of the moulds 74,10 occurring. This increases thepossibility of correct spacing being reliably achieved. As with thearrangement of the locking arms 32, it is necessary for the spacerdevices 109 to be set up by an operator when the apparatus is cold butthe spacer devices 109 must ensure proper spacing of the upper mould 74and the lower mould 10 at elevated temperatures during the press bendingoperation, which can entail inadvertent expansion or other deformationoccurring as a result of thermal cycling. The provision of three pairsof stop members 110, 116 ensures that the gap between the upper andlower mould 74,10 can reliably be set without any rocking of the uppermould 74 relative to the lower mould 10 in the final press bendconfiguration of the moulds 10,74.

It will be appreciated that in a typical tunnel furnace 2 a plurality ofcarriages 8 is provided, each containing a respective gravity bendingmould 10. A typical furnace 2 includes at least twenty carriage8/gravity bending mould 10 assemblies. However, only one press bendingupper mould 74 is provided. It is necessary in operation for each lowergravity bending mould 10 and its associated carriage 8 to be properlyset up with respect to the single upper press bending mould 74.Accordingly, the spacer devices 109 for defining the correct adjustablegap between the moulds 10,74 are provided in conjunction with eachrespective gravity bending mould 10 so that each gravity bending mould10 can be individually set up to operate correctly with the single uppermould 74. Each spacer device 109 is individually adjusted prior toinitial operation of the furnace so that during the press bendingoperation, when the upper mould 74 is lowered onto the glass sheets 4carried on the gravity bending mould 10, the upper and lower moulds74,10 are correctly spaced from each other a distance corresponding tothe thickness of the glass sheets 4 in their final bent form.

The press bending operation will now be described with reference to FIG.6. When the lower mould 10 carrying the glass sheets 4 thereon ispresented beneath the upper mould 74, the piston/cylinder assembly 94 isactuated so as to lower the support frame 80 supporting the upper mould74 until the upper mould 74 is in contact with the underlying glasssheets 4 on the gravity bending mould 10. The stroke of thepiston/cylinder assembly 94 is greater than that required just to causecontact of the upper mould 74 with the glass sheets 4. The support frame80 thus overtravels so as to continue to be lowered after contact of theupper mould 74 with the glass sheets 4 so that the support frame 80 hasbeen lowered so as to be nearer to the sub-frame 78 than in the initialconfiguration illustrated in FIG. 5. This over-lowering of the supportframe 80 causes the chains 82 to go slack. In this configuration, theupper mould 74 and its associated sub-frame 78 bear downwardly on theglass sheets 4 with the desired net weight which has been selected byappropriate selection of a particular weight for the secondcounterbalance 108. The upper mould 74 thus presses the upper surface ofthe glass sheets 4 with a predetermined net weight.

Moreover, since the upper mould 74 is not supported from above duringthe press bending operation at least towards the end of the pressbending operation, the weight of the upper mould 74 is uniformlydistributed across the entire abutting surfaces, typically over an areaof around 1 m², of the upper mould 74 and the underlying glass sheets 4.This ensures even weight distribution over the glass sheets 4 during thepress bending operation. The press bending operation typically lasts for20 seconds. Towards the end of the press bending operation in which theglass sheets have been pressed into intimate contact around their entireperiphery with the lower gravity bending mould 10 by the upper mould 74,for each of the spacer devices 109, the domed head 124 bears against theplate member 114 so as to define across substantially the entire area ofthe press bending mould a preset gap between the upper and lower moulds74,10 corresponding to the thickness of the press-bent glass sheets. Theprovision of the stop members ensures that over,pressing of the glasssheets 4 during the press bending operation does not occur. Thisminimizes edge marking of the lower surface of the glass sheets 4 by theannular rim 30 of the gravity bending mould 10 which is a particularproblem when employing a gravity bending mould having thin rims having athickness on the order of around 3 to 4 mm.

The spacer devices 109 are specially configured to accommodatevariations in the lateral positions of the upper mould 74 and the lowermould 10 because the domed head 124 can engage the plate member 114 overa selected range of lateral positions encompassed by the are of theplate member 114. This permits accurate spacing of the moulds to beachieved despite possible variations in the positions of the pluralityof gravity bending moulds 10 around the bending loop. This arrangementdoes not restrict the lateral freedom of the positioning of the upperdie 74 during press bending.

The upper mould 74 is supported by the support frame 80 by means of thechains 82 whereby the upper mould 74 is unconstrained against bothrotational and translational lateral movement, during the press bendingoperation. Moreover, the support frame 80 is suspended from the cable 86which in turn does not constrain the upper mould 74 against lateralmovement during the press bending operation. In addition, the supportingof the upper mould 74 by on the one hand a plurality of chains 82 to asupport frame 80 and on the other hand by a cable 86 between the supportframe 80 and the pulley 88 permits unconstrained vertical movement, forexample tilting, of parts the upper mould 74 during the press bendingoperation.

The upper mould 74 is required accurately to be positioned with respectto each of the plurality of the gravity bending moulds 10 in the entireloop including the tunnel furnace. In practice, the translationalposition, both horizontal and vertical, and the rotational position bothhorizontal and tilting, of each gravity bending mould 10 will vary fromone carriage to another not only following the initial set up of thefurnace but also, in particular, after operation of the furnace. This isdue to thermal expansion, deformation as a result of thermal cycling,and wear of the apparatus, for example wear of the carriage wheels onthe rails.

Since the upper mould 74 is permitted to nestle into the gravity bentshape of the glass sheets 4 during the press bending operation withoutany constraint on its lateral or tilting movement, the upper mould 74can readily find its correct position for accurate press bending withrespect to the underlying glass sheets 4 irrespective of the variationin position relative to the upper mould 74 of those glass sheets 4 fromone gravity bending mould 10 to another. This provision of freedom ofmovement of the upper mould 74 during the press bending operationensures that accurate press bending is achieved irrespective of anyvariations in positions between the plurality of lower gravity bendingmoulds. The suspension of the upper mould 74 by flexible members such aschains 82 permits this unconstrained movement.

In addition, the upper mould 74 is supported by the chains 82 wherebythe upper mould 74 can be rolled to a minor extent slightly into contactwith the underlying glass sheets 4. This provides that the requiredshape of the underlying glass sheets 4 can be achieved by a progressivepushing action as a result of the upper die progressively coming intocontact with the underlying glass sheets 4. Preferably, the upper mould74 is rolled onto the upper glass surface so that the deep bend portionsare first shaped by the upper mould 74.

The provision of the stop members in which the lower stop memberincludes a hemispherical dome and the upper stop member consists of aflat plate against which the dome bears ensures reliable relativevertical positioning of the upper mould and the lower mould so as tominimize inadvertent marking of the glass sheets by the gravity bendingmould 10. However this is achieved without removing or reducing theability of the upper mould 74 to move laterally both translationally androtationally and to tilt vertically relative to the lower mould 10 andthe glass sheets 4 in an unconstrained manner during the press bendingoperation.

Prior to the press bending operation, the underlying glass sheets 4 maybe heated by a roof heater so as to provides a differential temperatureprofile over the surface of the glass sheets 4 so as to assist the glasssheets 4 attaining the required shape during the press bendingoperation. Such a differential roof heating technique is described inco-pending European patent application No. 94309435.9.

The present invention can enable glass sheets to be manufactured withbend portions having radii as little as 150 mm. This may be compared toa minimum radius of 450 mm when gravity bending is employed usingdifferential heating of the glass sheets and a minimum radius of 1000 mmmm when employing gravity bending without differential heating.

The present invention enables glass sheets with deep bend portions to bemanufactured having edge stresses which compare to those achievableusing conventional sag bending techniques. The present inventiontypically enables bent glass sheets to be manufactured having edgetensile stresses, of less than 7 MPa. This enables glass sheets to bebent without requiring a subsequent anneal to remove stresses, followingthe press bending step.

What is claimed is:
 1. An apparatus for press bending glass sheets, theapparatus comprising an upper die, a suspension system for the upper diefor suspending and vertically moving the upper die, a lower gravitybending mould and a plurality of spacer devices for spacing the upperdie and the lower mould a selected distance from each other when theupper die presses a glass sheet on the lower mould, the suspensionsystem being arranged and the spacer devices being configured to permitsubtantially unconstrained lateral movement of the upper die relative tothe lower mould.
 2. An apparatus according to claim 1 wherein the spacerdevices each comprise a head member connected to one of the upper dieand the lower mould and a plate member connected to the other of theupper die and the lower mould, the head member having a range of spacerpositions encompassed within an area of the plate member.
 3. Anapparatus according to claim 2 wherein the head member has a domed head.4. An apparatus according to claim 2 wherein the head member isconnected to the lower mould and the plate member is connected to theupper die.
 5. An apparatus according to claim 2 wherein the head membercomprises a head of a threaded bolt which is threadably mounted to asupport body for the bolt whereby the head member can be adjusted inheight.
 6. An apparatus according to claim 1 comprising three of thespacer devices.
 7. An apparatus according to claim 6 wherein two of thespacer devices are located along a first edge of the lower gravitybending mould and one of the spacer devices is located along a secondedge opposite to the first edge of the lower gravity bending mould. 8.An apparatus according to claim 1 wherein the suspension systemcomprises a first counterbalance assembly connected to the die forproviding the die with a selected net weight, a frame mounted above thedie, a plurality of flexible members connecting the die to the frame forsuspending the die below the frame whereby the die is capable ofunconstrained lateral and tilting movement relative to the frame, and adie moving device connected to the frame for vertically moving the die.9. An apparatus according to claim 8 wherein the first counterbalanceassembly comprises a first pulley mechanism having one end and anopposite other end, the one end of the first pulley mechanism beingconnected to an upper surface of the die and the other end of the firstpulley mechanism being connected to a first counterweight.
 10. Anapparatus according to claim 8 wherein the flexible members comprisechains.
 11. An apparatus according to claim 10 wherein there are fourflexible members.
 12. An apparatus according to claim 8 wherein thefirst counterbalance assembly further comprises a rigid member extendingupwardly from an upper surface of the die.
 13. An apparatus according toclaim 8 wherein the first counterbalance assembly is connected to thecentre of an upper surface of the die.
 14. An apparatus according toclaim 8 wherein the die moving device comprises a piston and cylinderassembly.
 15. An apparatus according to claim 14 wherein the piston andcylinder assembly is pneumatically controlled.
 16. An apparatus forpress bending glass sheets, the apparatus comprising an upper die, asuspension system for the upper die for suspending and vertically movingthe upper die, a lower gravity bending mould and a plurality of spacerdevices for spacing the upper die and the lower mould a selecteddistance from each other when the upper die presses a glass sheet on thelower mould, the suspension system being arranged and the spacer devicesbeing configured to permit lateral movement of the upper die relative tothe lower mould, the suspension system comprising a first counterbalanceassembly connected to the die for providing the die with a selected netweight, a frame mounted above the die, a plurality of flexible membersconnecting the die to the frame for suspending the die below the framewhereby the die is capable of unconstrained lateral and tilting movementrelative to the frame, and a die moving device connected to the framefor vertically moving the die, and including a second counterbalanceassembly between the frame and the die moving device, the secondcounterbalance assembly including a second pulley mechanism having oneend and an opposite other end, the one end of the second pulleymechanism being connected to the frame and the opposite other end of thesecond pulley mechanism being connected to a second counterweight, thesecond counterweight being connected to the die moving device.
 17. Anapparatus according to claim 16 wherein the first and secondcounterbalance assemblies are mounted on a common side of a tunnelfurnace containing the die.
 18. A method of press bending glass sheets,the method comprising the steps of providing a glass sheet which isgravity bent and carried on a gravity bending mould; lowering an upperdie onto the glass sheet by a suspension system which supports the upperdie, the upper die having a lower surface to mould the glass sheet to adesired curved shape, and releasing the upper die from being supportedby the suspension system so that the upper die rests on the glass sheetat a selected net weight during a press bending operation, the upper diebeing spaced above the gravity bending mould which comprises a lower dieby a predetermined distance defined by a plurality of spacer devices;and wherein during the lowering step the upper die is unconstrainedagainst lateral and tilting movement so that the upper die is permittedprogressively to be aligned with the glass sheet as the upper die comesinto contact with the glass sheet, the spacer devices being arranged topermit said lateral and tilting movement of the upper die.
 19. A methodaccording to claim 18 wherein the spacer devices each comprise a headmember connected to one of the upper die and the lower die and a platemember connected to the other of the upper die and the lower die, thehead member having a range of spacer positions encompassed within anarea of the plate member.
 20. A method according to claim 19 wherein thehead member has a domed head.
 21. A method according to claim 18comprising three of the spacer devices.
 22. A method according to claim21 wherein two of the spacer devices are located along a first edge ofthe gravity bending mould and one of the spacer devices is located alonga second edge opposite to the first edge of the gravity bending mould.